Cured polymers of alpha-olefins and their preparation



United States Patent 25 Claims. (Cl. 260-795) This invention relates toa method for curing (i.e., cross-linking) normally solid polymers andcopolymers of a-olefins and to the cured products obtained thereby. Moreparticularly, this invention relates to a novel method for curingnormally solid polypropylene and the cured product thereof.

In accordance with this invention, a normally solid polymer or copolymerof an alpha-olefin is cured by heating, at an elevated temperature, acomposition comprising the polymer to be cured in mixture with a smallamount, based on the weight of the polymer, of a tetrahaloquinone or ofsulfur and a tetrahaloquinone as the curing agent. In more specificembodiment, the invention is carried out by heating a mixture comprising100 parts by weight of a polymer or copolymer to be cured, from about0.5 to about parts by weight of a tetrahaloquinone and from 0 to about2.5 parts by weight of sulfur, the sulfur being in an amount from zeroup to about one half the weight of the curing agent.

Still more specifically, and although the amount of the tetrahaloquinonecuring agent that is used will depend on the particular tetrahaloquinoneand polymer or c0- polymer to be cured, a more preferred mixture to becured contains from about 1 to about 4 parts by weight of the curingagent per 100 parts by weight of the polymer or copolymer. Theproportion of sulfur in the mixture will also depend on the particularcuring agent and polymer or copolymer employed with the preferredproportion generally being less than half the weight of that of thecuring agent and, generally, from about 0.5 to about 2 parts by Weightper 100 parts by weight of the polymer or copolymer, although thepresent invention is operable with no sulfur in the curing compound.

In a particular embodiment of the present invention, the polymer orcopolymer to be cured is ground and slurried with the curing agent andsulfur, if desired, in an organic liquid, suitable examples of whichinclude acetone, diethyl ether, and others, with the compounding beingaccomplished by evaporating the solvent. Thereafter the composite isdried at about ZOO-250 F. The polymeric composition can then be cured byheating at an elevated temperature, as for example, from about 275 toabout 425 F., and more specifically, from about 325 to about 375 F. fora length of time sufiicient to allow adequate curing, usually for atleast about 3 minutes and, generally, from about 5 to about 60 minutes.

The above-described method is suitable for a smallscale application ofthe method of the present invention. The present method, however, may beapplied similarly in a larger scale. In such an application thecompounding is achieved on conventional roller mills or in internalmixers such as a Banbury, Koneader or screw extruders, particularly thetwin screw extruder, and the like. In all cases the final temperature ofthe batch should be as low as practicable, preferably exceeding onlyslightly the melting point of the polymer. Although maximum temperaturesof the order of about 425-450 F. are encountered in the mixing cycle,preferably themixer employed discharges the compound at a temperaturecon- "ice siderably lower. Significantly, many of the above internalmixers are particularly effective in dispersing the compoundingingredients. Consequently, in such a process, the mixing time would befrequently shortened to about 3-5 minutes and would rarely exceed 5-10minutes.

The present invention is especially applicable to the curing ofpolypropylene and, hence, the invention is described herein withparticular emphasis on polypropylene. However,it is also applicable tothe curing of other polymers or copolymers of alpha-olefins, forexample, polymers or copolymers obtained from one, two or more of thefollowing olefins: ethylene, propylene, l-butene, lpentene,4-methyl-l-pentene, S-methyl-l-hexene, 4-ethyll-pentene, and, ingeneral, other alpha-olefins containing up to 10 carbor atoms. Inreference to copolymers, it is preferred that one of the olefins fromwhich the copolymer is obtained be ethylene or'propylene. Additionally,the invention is applicable to the curing of a broad spectrum ofcopolymer compositions including terpolymers and higher combinations. Incommercial. practice with polymers of particularly beneficial utility,the copolymers most frequently comprise ethylene, propylene, l-butene orcombinations thereof. With more difliculty, the invention is alsoapplicable to the curing of a copolymer of one of the above-mentionedalpha-olefins and another olefin having a double bond which is not inthe alpha position. Examples of such other olefins include thefollowing: Z-butene, Z-pentene, Z-hexene, 3-hexene, and others.

The tetrahaloquinones useful for practice of the present invention havethe following formula:

wherein X X X and X are halogen atoms, examples of which include:chlorine, bromine, iodine or mixtures thereof, and preferably, chlorine.Specific examples of useful tetrahaloquinones are chloranil(tetrachloroquinone), tetrabromoquinone, trichlorobromoquinone, andothers.

By the method of the present invention, polymers or copolymers ofalpha-olefins can be cured to give products having a high tensilestrength, e.g., from about 4000- 5 500 p.S.i. atyield, an elongation atbreak of about 3.5- or more, while exhibiting excellent chemicalinertness.

The following examples set forth embodiments of the invention forpurposes of illustration and not limitation.

Example (A) In this example polypropylene, chloranil (CL) and,

sulfur were combined according to the following formulas (all partsbeing by weight):

Slabs of the composition of Formula A were cured at various curingtemperatures. The physical properties of the various products wereevaluated and the results are given below;

A-l A-2 A-8 A-4 A-5 A-G A-7 A-8 Curing temperature, F 325 330 335 340350 360 370 335 Curing time, minutes at yield 30 30 30 30 30 30 30 60Tensile strength at yield, p.s.i 500 4970 5250 3970 3520 3370 5040Tensile modulus, p.s.i 200, 000 209, 000 211, 000 266, 000 228, 000 235,000 202, 000 240, 000 Elongation, percent. 7 1 70 10 3.5 4 4. 6. 5 Gel,percent 40 52 55 66 50 55 48 70 results are given below:

B1 B-2 I 13-3 Curing temperature, F 330 340 350 Tensile strength atyield, p. 5470 4800 4600 Tensile modulus, p.s.i 246, 000 192, 000 173,000 Elongation, percent 11 100 100 Gel, percent 53 25 The above resultsclearly illustrate that a polymer of an alpha olefin, exemplified bypropylene, compounded with a tetrahaloquinone or with a tetrahaloquinoneand sulfur can be effectively cured to give a cross-linked product whichexhibits superior strength, ductility and chemical inertness.

Although the present invention has been described with preferredembodiments, it is to be understood that modifications and variationsmay be resorted to, without departing from the spirit and scope of thisinvention, as those skilled in the art will readily understand. Suchvariations and modifications are considered to be within the purview andscope of the appended claims.

What is claimed is:

1. A method for curing normally solid polymers of an alpha-olefin whichcomprises heating a normally solid polymer of an alpha-olefin, blendedwith a small amount, based on the weight of said polymer, of atetrahaloquinone as a curing agent, at a temperature above the meltingpoint of said blend, for a period of time sufiicient to cross-link saidpolymer.

2. A method for curing normally solid polymers: of an alpha-olefin whichcomprises heating a normally solid polymer of an alpha-olefin, blendedwith a small amount, based on the weight of said polymer, of atetrahaloquinone as a curing agent, and sulfur in an amount by weightless than that of said curing agent, at a temperature above the meltingpoint of said blend, for a period of time suflicient to cross-link saidpolymer.

3. A method as defined in claim 1 in which the blendby weight contains0.005 to about 0.05 part of the tetrahaloquinone per part of thepolymer.

4. A method as defined in claim 1 in which the blend by weight contains0.005 to about 0.05 part of the tetra haloquinone and sulfur in anamount up to about /2 the weight of the tetrahaloquinone.

5. A method as defined in claim 1 wherein the blend is heated at atemperature of from about 275 F. to about 425 F. for at least 3 minutes.

6. A method as defined in claim 2 wherein the blend is heated at atemperature of from about 275 F. to about 425 F. for at least 3 minutes.

7. A method as defined in claim 1 wherein the blend by weight contains0.005 to about 0.05 part of the tetrahaloquinone per part of thepolymer, and wherein the blend 1S heated at a temperature of from about275 F. to about 425 F. for at least 3 minutes.

8. A method as defined in claim 1 wherein the normally solid polymer ispolypropylene.

9. A method as defined in claim 2 wherein the normally solid polymer ispolypropylene.

10. A method as defined in claim 1 wherein the normally solid polymer isa copolymer of two or more different alpha-olefins.

11. A method as defined in claim 1 wherein the normally solid polymer isa copolymer of an alpha-olefin and an olefin unsaturated other than inthe alpha position.

12. A method as defined in claim 1 wherein the tetrahaloquinone has thefollowing structure:

in which X X X and X are halogen atoms.

13. A method as defined in claim 1 wherein the tetrahaloquinone curingagent is chloranil.

14. A method as defined in claim 2 wherein the tetrahaloquinone curingagent is chloranil.

15. A composition, useful in the preparation of cured polymers ofalpha-olefins, comprising a normally solid polymer of an alpha-olefin,blended with a small amount, based on the weight of said polymer, of atetrahaloquinone as a curing agent.

16. A composition, useful in the preparation of cured polymers ofalpha-olefins, comprising a normally solid polymer of an alpha-olefin,blended with a small amount, based on the weight of said polymer, of atetrahaloquinone as a curing agent, and sulfur in an amount less thanthat of said curing agent.

17. A composition, useful in the preparation of cured polymers ofalpha-olefins comprising a blend as defined in claim 15 which containsby weight from about 0.005 to about 0.05 part of said tetrahaloquinoneper part of said polymer.

18. A composition, useful in the preparation of cured polymers ofalpha-olefins comprising a blend as defined in claim 16 which containsby weight from about 0.005 to about 0.05 part of said tetrahaloquinoneper part of said polymer and sulfur in an amount up to about /2 theWeight of said tetrahaloquinone.

19. A composition, useful in the preparation of cured polymers ofalpha-olefins, comprising a blend as defined in claim 17 wherein thenormally solid polymer is polypropylene.

20. A composition, useful in the preparation of cured polymers ofalpha-olefins, comprising a blend as defined in claim 16 wherein thenormally solid polymer is polypropylene.

21. A composition, useful in the preparation of cured in claim 15wherein the tetrahaloquinone has the follow- 25. A composition, usefulin the preparation of cured ing structure: polymers of alpha-olefins,comprising a blend as defined in X2 claim 16 wherein thetetrahaloquinone curing agent is I l chloranil.

5 References Cited by the Examiner UNITED STATES PATENTS 6 2,890,1876/1959 Bowman et a1 26079.5 X3 X 2,920,062 1/1960 McFarland 26079.5 inwhich 1 2 3 and 4 are halogen atoms. 2,983,714 5/1961 Robinson et a1.260-79.5 24. A composition, useful in the preparation of cured 103,047,552 7/ 1952 Reynolds et a1 260-949 polymers of alpha'olefins,comprising a blend as defined in claim 15 wherein the tetrahaloquinonecuring agent in JOSEPH SCHOFER Pnmary Exammer' chloranil. L. EDELMAN,Assistant Examiner.

1. A METHOD FOR CURING NORMALLY SOLID POLYMERS OF AN ALPHA-OLEFIN WHICHCOMPRISES HEATING A NORMALLY SOLID POLYMER OF AN ALPHA-OLEFIN, BLENDEDWITH A SMALL AMOUNT, BASED ON THE WEIGHT OF SAID POLYMER, OF ATETRAHALOQUINONE AS A CURING AGENT, AT A TEMPERATURE ABOVE THE MELTINGPOINT OF SAID BLEND, FOR A PERIOD OF TIME SUFFICIENT TO CROSS-LINK SAIDPOLYMER.
 12. A METHOD AS DEFINED IN CLAIM 1 WHEREIN THE TETRAHALOQUINONEHAS THE FOLLOWING STRUCTURE: